Electrical condenser



y 1, 1956 H. M. WADSWORTH 2,744,221

ELECTRICAL CONDENSER Filed Jan. 26, 1953 2 Sheets-Sheet l IN V EN TOR. y /vu/ur-d fil. ZZ/ZZ dSH/OWUL WITNE S A ORNEY May 1, 1956 H. M. WADSWORTH 2,744,221

ELECTRICAL CONDENSER Filed Jan. 26, 1953 2 Sheets-Sheet 2 IN V EN TOR. fi/owaldm. iflimiswvrZ/u WITNESS:

AT ORNEY United States Patent ELECTRICAL CONDENSER Howard M. Wadsworth, Liverpool, N. Y. Application January 26, 1953, Serial No. 333,035 3 Claims. (Cl. 317-249) The present invention relates to an electrical condenser and more particularly to a'trimmer condenser for high frequency oscillating electrical circuits.

Electrical condensers of the above type are now commonly constructed by metallizing the exterior of a small dielectric tube to form one plate of the condenser, while a cylindrical metal slug is movably mounted in the interior of the tube to form the other condenser plate.

The dielectric tubes, which are usually made of glass, are subject to significant deviations from true cylindricity, and the traversing means for the inner electrode are often considerably out of line with the axis of the tube. This makes it difficult to produce an inner electrode having full surface contact with the interior of the tube which will not be liable to break the tube when the electrode is adjusted axially.

It is an object of the present invention to provide a novel trimmer condenser of the above type having an inner electrode formed of sheet metal which is yieldably pressed outward into substantially full surface contact with the inner surface of the dielectric tube.

it is another object to provide such a trimmer in which the inner electrode is traversed longitudinally with little or no rotary movement Within the dielectric tube.

It is another object to provide such a trimmer in which the traversing means for the inner electrode is so constructed as to yieldingly permit some lateral movement of said electrode to accommodate for misalignment in the tube.

It is another object to provide such a trimmer which is free from microphonics such as might be caused by loosely sliding contacts.

It is another object to provide such a trimmer in which the expansive force of the inner electrode may be readily adjusted.

It is another object to provide such a device in which the inner electrode is so formed as to slide smoothly in the tube without any tendency to jam in constrictions or deformations of the tube.

It is another object to provide such a device which is economical to manufacture and assemble, easy to adjust, and which maintains its adjustment securely in spite of vibration or shock.

Further objects and advantages will be apparent from the following description taken in connection with the accompanying drawing, in which:

Fig. l is a side elevation of a trimmer condenser embodying a preferred form of the invention partly broken away and in section;

Fig. 2 is an end view of the same;

Fig. 3 is an enlarged detail of the inner electrode illus trated in Fig. 1 shown partly in elevation and partly in section; a

Fig. 4 is a view similar to Fig. 1 showing a second embodiment of the invention;

Fig. 5 is a top view of Fig. 4;

Fig. 6 is an enlarged detail in perspective showing the inner electrode of Fig. 4 with the end compression discs removed;

Fig. 7 is an enlarged detail of an inner electrode similar to that shown in Fig. 4, with a modified form of end compression discs; and

Fig. 8 is a detail in perspective of one of the compression discs shown in Fig. 7.

In Fig. l of the drawing there is illustrated a trimmer condenser comprising an outer electrode 1 which is in the form of a metallized coating of a dielectric tube 2 of suitable material such as glass. The electrode 1 is provided with a soldered lead 3 for convenient connection with its intended circuit.

An inner electrode 4 is slidably mounted Within the dielectric tube 2 for movement into and out of telescopic relation with the outer electrode 1. As best shown in Fig. 3, the inner electrode 4 is in the form of a longitudinally split cylinder having a plurality of tapering tabs or fingers 5 on each end. The inner electrode is made from a sheet of moderately elastic metal such as brass or bronze, and the tabs 5 are curved inwardly to form elastic abutments at the ends of the electrode.

Means for adjusting the inner electrode longitudinally in the tube 2 are provided comprising a shaft 6 which is threaded for a portion of its length and traverses a nut 7 rigidly connected to the end of the tube 2 as by means of metallizing and soldering as indicated at 8. The nut 7 is formed'with a shoulder 9 and is externally threaded as shown at 11 for the reception of a clamping ring 12 by which the nut 7 may be rigidly mounted in a panel 13.

The shaft 6 is formed with portions of reduced diameter forming shoulders 14 and 15' which are spaced apart a distance somewhat less than the free over-all length of the inner electrode 4. Said electrode is mount ed on the shaft by telescoping it over the end of the shaft and then compressing the electrode endwise until the tabs 5 at each end are forced in between the shoulders 14, 15 which thereafter hold the electrode under pres-,

sure. This endwise pressure produces a tendency for the body of the electrode to spring outwardly so that when it is inserted in the tube 2, the electrode has substantially full surface contact with the interior of the tube.

if the tube should be slightly oval-shaped or tapered, the elasticity of the electrode 4, together with the endwise pressure under which it is assembled causes it to maintain its close contact with the tube in spite of such irregularities. if the nut 7 is not perfectly aligned with the bore of the tube, the shaft 6 may wobble slightly as it is rotated to adjust the position of the electrode, but this relative movement is permitted by the sliding of the ends of the tabs 5 on the radial shoulders 14, 15 without affecting in any way the bearing of the electrode in the tube. Since the tabs 5 bear on said shoulders with quite high unit pressures, good electrical contact is maintained at all times so that microphonics are prevented.

Since the bearing of the inner electrode 4 in the tube 2 is of much larger area and at a much greater radius than the bearing between said electrode and the shaft 6, it is obvious that the electrode will be prevented from rotation. with said shaft, and will have a direct longitudinal traversing motion. This is desirable in that it eliminates the possibility of irregularities or loop-backs in the capacity-displacement curve of the trimmer, which might oc cur if the electrode should rotate as it is traversed. Actually, any small departure from true cylindricity of the tube may, in the present structure, become an advantage by ensuring such direct traversal of the electrode.

In the embodiment of the invention illustrated in Figs. 4-, 5 and 6 the outer electrode, tube and mounting means are the same as in the first embodiment. In this structure however the adjusting shaft 16 is threaded throughout its length, and a sleeve or core- 17 of elastically deformable material such as rubber having a normal diameter sli htly less than the interior of the tube 2 is mounted adjacent the inner end of said shaft. The inner electrode 18 is here shown in the form of a band of sheet metal wrapped around the core 17 with the ends of the band bent inward as shown at 19 and 21 in Fig. 6 to enter loosely into a longitudinal slot 22 formed in the core.

Means are provided for causing the inner electrode to more longitudinally with the shaft 16, and also to expand the inner electrode into full contact with the interior of the tube. As shown in Fig. 4, this is accomplished by means of nuts 23, 24 threaded on the shaft 16 at each end of the electrode and tightened up to compress the core 17 sufficiently to secure the desired expansive pressure for the electrode 18. The nuts 23, 24 are preferably provided with saw-tooth shaped dentals on their sides which are arranged to penetrate the core 17 and prevent the nuts from loosening. The electrical connection between the electrode and shaft 16 may be secured by bending down a tab 25 to make contact with one of the nuts or in any other suitable manner.

in Fig. 7 the inner electrode 13 is the same as illustrated in Fig. 4, but the expanding means is in the form of a pair of annular discs 26, 27 having inwardly extending elastic tongues 28, 29 having slanting engagement with the surface of the shaft 16 to hold the discs compressed against the elastic core 17. In this case, the end of the shaft carrying the electrode may if desired be provided with annular grooves 31 instead of threads.

in all the embodiments of the invention illustrated, the capacity of the trimmer is adjusted by rotation of the shaft 6 or 16 in any suitable manner, the nut 7 remaining stationary whereby the overlapping relation of the inner and outer electrodes is varied to secure the desired capacity. When so adjusted, the elastic pressure of the inner electrode against the inner wall of the dielectric tube maintains the adjustment securely.

It will be understood that in the embodiment illustrated in Figs. 4 to 8, the lateral movement of the shaft with respect to the inner electrode necessary to compensate for misalignment is permitted by the elasticity of the core 17.

Although certain embodiments have been shown and described in detail it will be understood that changes may be made in the precise form and arrangement of the parts illustrated without departing from the spirit of the invention.

What is claimed is:

l. in a trimmer for high frequency oscillating electrical circuits a stationary cylindrical dielectric tube, an outer electrode fixedly mounted thereon, an inner electrode comprising a split hollow cylinder of elastic sheet metal, and means for longitudinally adjusting the inner electrode, said adjusting means including means to apply axial pressure to the ends of the inner electrode, said inner electrode having means whereby said axial pressure expands it into substantially full surface contact with the interior of the tube.

2. A trimmer condenser as set forth in claim 1 in which the inner electrode is provided at both its ends with inwardly-bent elastic tabs, and the adjusting means comprises a shaft having a pair of opposing shoulders spaced slightly less than the over all free length of the inner electrode, between which shoulders the inner electrode is held under axial compression.

3. A trimmer condenser as set forth in claim 2 in which the shoulders on the adjusting shaft extend radially and the elastic tabs of the inner electrode bear on said shoulders at points suificiently spaced from the body of the shaft to permit lateral aligning movement of the inner electrode without varying its axial compression between the shoulders.

References Cited in the file of this patent UNITED STATES PATENTS 2,318,415 Patzschke May 4, 1943 FOREIGN PATENTS 230,615 Great Britain Mar. 19, 1925 602,270 Germany Sept. 5, 1934 628,499 Germany Apr. 6, 1936 976,251 France Oct. 25, 1950 

